The focus of this project will be to develop novel virus-like particle (VLP)-based immunogens for eliciting strong neutralizing antibody responses against severe acute respiratory syndrome (SARS) coronavirus. Previous studies with coronaviruses have shown that co-expression of the M and E glycoproteins can lead to the formation of virus-like particles and their release from the cell. Furthermore, when the spike (S) protein is expressed along with the M and E proteins, it can be incorporated into the coronavirus VLPs. We plan to achieve our goals in three phases. First, based on the results obtained in our preliminary studies and our experience in VLP design and production, we will develop "first generation" SARS CoV VLPs consisting of its M, E and S proteins or "first generation" chimeric VLPs formed by SIV Gag proteins that incorporate high levels of SARS CoV S proteins. Second, we will investigate whether VLPs formed by other viral core proteins will provide a better framework for the development of VLP-based vaccines against SARS. Third, we will explore alternative approaches to develop "second generation" phenotypically mixed VLPs to enhance their immunogenicity. Specifically, we will focus on two promising strategies: 1) To design phenotypically mixed VLPs for targeting to antigen-presenting cells to augment immune responses (ligand for fit3, mannose receptor); and 2) To design phenotypically mixed VLPs for targeting to mucosal surfaces to enhance mucosal immune responses (inclusion of HA, HN). Through this systematic approach, we will explore different strategies to design and produce novel SARS VLPs, compare their efficacies in inducing immune responses in small animal models and determine optimal immunization routes (mucosal immunization by intranasal route vs. systemic immunization via intramuscular injection), with the aim to develop candidate vaccines for large-scale production.